Level select:
Hold [Left Shift] while selecting the "New Game" option. Any level
except for "Limbs, Heads And Smoking Craters" or "A Long Awaited
Drinking Party" may be selected for game play.

Kill animals:
Hold [Command] + [Shift] + [Option] and click on an animal.

Lose current level:
Hold [Ctrl] + [Keypad Minus] during game play in single player mode.

Win current level:
Hold [Ctrl] + [Keypad Plus] during game play in single player mode.

Limbs, Heads and Smoking Craters level:
Exit level 20, "Murder of Crows" through the northeast corner.

A Long Awaited Drinking Party level:
Kill the three frogs in the northeast corner before completing level 3,
"Down A Broken Path"